1. Field of the Invention
The present invention relates to an automatic focusing mechanism for mounting on (or integrating into) a measuring device such as an electronic level or the like, the mechanism having a telescope for sighting a leveling rod (or staff).
2. Description of the Related Art
Conventionally, as a measuring device of this kind, Published Examined Japanese Patent Application No. 184042/1993 discloses a level which is a measuring device provided with a telescope. The level sights, by the telescope, a leveling rod which has marked thereon bar codes. A comparison is then made between a bar code pattern which is stored in advance and the sighted bar code to thereby obtain a sighted position. The level is provided therein with a photoelectric device for converting the sighted image into an electric signal. A focusing lens for forming an image of the sighted image onto the photoelectric device is manually operated to thereby move the focusing lens in a back and forth direction.
This conventional measuring device has the following disadvantages. Namely, since the focusing operation must be performed manually, it takes time to finish the focusing operation. Furthermore, the time required to complete the focusing operation depends largely on the skill of a surveyor who performs the focusing operation. In the field of a camera or the like, there are known a plurality of automatic focusing mechanisms. In each of the automatic focusing mechanisms, an optical mechanism such as a sensor, mirror or the like which is specially prepared for the purpose in question is required. In order to add this kind of automatic focusing mechanism to the conventional measuring device, a large modification or addition to the conventional mechanism is required, resulting in an increase in the cost.
In view of the above-described problem, the present invention has an object of providing an automatic focusing mechanism which is capable of performing the focusing on the leveling rod without the necessity of large modification to the conventional measuring device.